CheyTac LLC Intervention

The CheyTac Intervention is an American bolt action sniper rifle manufactured by CheyTac LLC for long range soft target interdiction. It is fed by a detachable single stack magazine, which holds 7 rounds. It fires .408 CheyTac or .375 CheyTac ammunition. CheyTac papers state that the entire system is capable of delivering sub-MOA accuracy at ranges of up to 2,500 yards (2,300 m), one of the longest ranges of all modern-day sniper rifles. It is based on the EDM Arms Windrunner.

CheyTac L.L.C researched the optimum cartridge case, bullet and barrel configuration for very long range use. For this the .408 Chey Taccartridge was developed that fires very-low-drag mono metal bullets that were specially designed for the Long Range Rifle System by the now (2010) defunct company, Lost River Ballistic Technologies.

Lost River Ballistic Technologies inventor, Mr. Warren Jensen, stated that "the .408 Chey Tac was the first bullet/rifle system that utilizes a balanced flight projectile. To achieve balanced flight the linear drag has to be balanced with the rotational drag to keep the very fine nose (meplat) of the bullet pointed directly into the oncoming air. It should result in very little precession and yaw at extreme range and allows accurate flight back through the transonic region. This is hard to achieve for small arms projectiles. Mathematically you are at a great disadvantage trying to achieve balanced flight with a lead core non mono metal bullet. The rotational mass/surface area ratio is too high."

The balanced flight projectile patent can be found at the US Patent Office, Controlled spin projectile, US PAT No. 6,629,669. According to the patent, a projectile engraved and launched according to the specifications of the patented invention should decelerate from supersonic flight through transonic to subsonic in a stable and predictable manner effective to a range beyond 3,000 yards (2,743 m). It implies that, amongst several other preconditions, the rifle barrel has to have specific rifling dimensions to achieve a desired amount of axial air drag on the bullet's surface, which reduces the bullet's spinrate to achieve balanced flight.

To achieve balanced flight the rifling twist rate for the .408 CheyTac chambering was chosen at 330.2 mm (1 in 13 in), with eight 0.4080 in diameter grooves, 0.4010 in diameter bore and a 0.050" land width, square cut, with no taper. The later .375 CheyTac round, developed from the .408 CheyTac, uses a 292 mm (1:11.5 in) rifling twist rate.

(Sources from Wikipedia)